Many different kinds of communication systems, including, but not limited to, direct conversion products such as wireless system receivers, and GSM systems, transmit data using so-called Quadrature Amplitude Modulation, or QAM, over two different out-of-phase channels. These channels are conventionally referred to as the in-phase channel or “I” channel, and the quadrature phase channel or “Q” channel. In such a system, both the in-phase signal, and the 90° out of phase quadrature signal, are used to completely restore a desired signal. Any errors between the matching of the channels can affect the received signal, and hence can cause errors in the received signal.
In receivers of this type, there will always be mismatches between the components used in the I and Q channels. A filter or compensation can be used in an attempt to compensate for the mismatches.